The strain follower industry is crowded with numerous designs of extensometers, compressometers and deflectometers each specifically designed to handle numerous conditions of static or dynamic testing, tension or compression, varying temperatures, specimen size and shape and other specific applications. Of the known strain followers available prior to the present invention, the vast majority of strain followers are utilized as laboratory instruments for use in controlled environments where large vibrations and abuses of the industrial workplace are avoided. Furthermore, the controlled laboratory environment subjects test specimens, typically, to purely axial loads (compression or tension) or to deflection imposed by forces moved through a single plane.
The industrial workplace does not represent such an easily controlled environment. Machine components are constantly exposed during operation to large vibrations; machine parts do not come in prepared, test specimen sizes of the laboratory; the magnitude of forces on machine components is not always controllable or predictable; machine components are subjected, often times, to combinations of axial forces, bending forces, torsional forces and deflection forces which are not always predictable.
While attempting to perform strain measurements and, thus, determine the amount of force exerted on the machine components of an operating machine within an industrial environment, at least some industrial users have found existing strain followers to be woefully inadequate in addressing the needs within the operating environment. Some particular problems include, but are not limited to: background noises which overshadow the output signals from the existing strain followers; excessive bending forces, especially in compression situations, which could not be compensated for by the existing strain followers; torsional forces acting on machine elements, which torsional forces can not be compensated for by the existing strain followers and, thus, complicate the measurement of pure axial strains. One example of an industrial application wherein preexisting strain followers appear to have proven inadequate, is the measurement of strain (for purposes of determining axial force) imposed upon a valve stem operating within a flow control system in a nuclear power plant.
A surprising and welcome step towards solving the problems experienced in the industrial environment was taken by the introduction of the Stem Strain Transducer which is the subject of the parent U.S. patent application to which this specification is a continuation-in-part. The Stem Strain Transducer provided inventive concepts which, at least, minimized the impact of torsional forces on measurements of axial strain; provided a practical approach to the compressive, bending forces realistically encountered in industrial operations; and introduced a rugged design capable of withstanding the industrial environment. Without detracting from the value of the Stem Strain Transducer and its inventive breakthroughs, the present invention has sought to improve upon the Stem Strain Transducer, especially in the manner in which this inventive strain follower compensates for background noise of the industrial environment and, in the low-end sensitivity of the present invented device.